1. Field of the Invention
This invention relates to a charged beam irradiating apparatus which is, for example, used for manufacturing semiconductor devices and also relates to a cleaning method of the apparatus.
2. Description of the Related Art
Recently a charged beam irradiating apparatus, for example electron beam exposure apparatus, is used for forming desired patterns of semiconductor devices on a semiconductor substrate or is used for making a mask substrate. As one of the important parts, the apparatus has electrostatic deflectors for scanning and focusing the electron beam. The advantage of the electrostatic deflectors is that they don't have hysteresis, compared with magnetic deflectors, and they have a characteristic of quick response to input signals.
However, a kind of contamination tends to deposit on the surface of the deflectors. Because the deflectors are positioned close to the path of the electron beam, the contaminations cause the deflectors to charged up and they thus deteriorate the performance of the deflectors.
The contaminations are mainly an organic material made from residual gasses in the vacuum chamber of the apparatus. The residual gasses are dissociated by the irradiation of the electron beam and are polymerized on the surface of the deflectors. As a result, the contaminations are formed on the surface of the deflectors.
To prevent the formation of the contaminations, some counter measures are made. For example, there is provided a method for improving the vacuum pressure of the chamber or a method for decreasing scattered electrons of the beam by using a shaped aperture, which limits the electron beam, with a thin knife edge.
However, the formation of contaminations cannot be prevented completely regardless of these counter measures. Therefore, the deflectors must be removed from the apparatus to be cleaned or exchanged frequently. Without the cleaning or the exchanging, the contaminations become a cause of decreasing performance and they lead to the deterioration of exposure accuracy or through put.
The contaminations cannot be easily removed by organic solvents, and are usually cleaned off by decomposing abrasives. This cleaning method makes the operating rate of the apparatus extremely low, and increases the personnel expenses necessary for the disassembly, cleaning and reassembly of the apparatus.
Also, the cleaning method using the abrasives cannot be used if part of the apparatus has a possibility of receiving damage to its surface material.
The contaminations are also observed on the surface of other parts exposed by the electron beam, such as apertures, electrical lenses, electrodes of the electric gun, a substrate or the inner surface of an optical column. These parts also need to be cleaned or exchanged.
So a simpler and more effective method for removing the contaminations is desired.
To prevent the problem, a method for removing the contaminations is presented. That is, a high frequency voltage is given between the inner surface of the optical column and an electrode which is inserted along the inner portion of the column.
Reactive gasses, such as CF.sub.4, O.sub.2 are introduced into the column and a gas plasma is generated in the column. As a result, the contaminations on the inner surface of the column are removed. After this, the exposure process is resumed (Japanese patent application, KOKAI No. 61-20321).
However, this method has another problem in that the material of the apparatus is damaged by the plasma. Especially, the damage to the electrostatic deflectors is a serious problem. The causes of the damage are thought to be ion impacts of the plasma or temperature increase of the parts by the impacts.
The same problem as the electron beam exposure apparatus occurrs in a scanning electron microscopy, an electron beam tester, an ion beam irradiating apparatus, or other apparatuses which use beams of charged particles.